a. Multi-Pulse Thyristor Rectification System: Achieves relatively ideal current and voltage harmonics through single-phase shifting rectification technology with a single 12-pulse system or 24-pulse system. In a single 12-pulse system, the current harmonics range from 12% to 14%, and the voltage harmonics are around 1.2%. In a single 24-pulse system, the current harmonics drop to 5-6%, and voltage harmonics are reduced to 0.9%. The multi-pulse thyristor rectification system incorporates on-load tap changers in the rectifier transformer to conveniently adjust the valve-side voltage. This system maintains a power factor greater than or equal to 0.95 and efficiency exceeding 98.5%. There are various transformer configurations available for the multi-pulse thyristor rectification system, including 6-pulse three-phase five-column dual-star structure, 6-pulse three-phase dual-star with balanced reactors, valve-side star-delta phase-shifting 12-pulse structure, grid-side phase-shifting combined with valve-side star-delta phase-shifting 24-pulse structure, and grid-side autotransformer-adjusted 24-pulse structure.
b. Three-Phase Bridge Diode Rectification + IGBT Chopping System: The power factor can reach 0.96 or higher, with efficiency exceeding 98.5%. The rectifier transformer has a simple structure, usually without on-load tap changers, making it a mature, reliable, and cost-effective solution. It can meet the current requirements of 500-1000 Nm3/h ALK electrolyzers and 200-500 Nm3/h PEM electrolyzers.
c. Three-Phase Bridge IGBT PWM Rectification + DC/DC Chopping Solution: The PWM rectification circuit ensures current harmonics below 3%, power factor exceeding 0.99, and efficiency exceeding 99.0%. The rectifier transformer has a straightforward structure and typically does not require on-load tap changers. It is suitable for hydrogen production applications in the range of 500-1000 Nm3/h for ALK electrolyzers and 200-500 Nm3/h for PEM electrolyzers. This solution is applicable to new energy hydrogen production scenarios, such as photovoltaic and wind power, where the power source is unstable. However, it currently comes with higher costs and lower cost-effectiveness.